The present invention relates to archery bows, and more particularly to a cam system and related components for compound archery bows.
Conventional compound archery bows include a bowstring and a set of power cables that transfer energy from the limbs and cams or pulleys, both generally referred to as “cams” herein, of the bow to the bowstring, and thus to an arrow shot from the bow. The power cables and bowstring may be strung from one cam on one limb to another cam on another limb of the bow. The function of the cams is to provide a mechanical advantage so that energy imparted to the arrow is a multiple of that required of an archer to draw the bow.
Generally, there are single cam systems and dual cam systems, with various configurations of each. A single cam system usually includes a single cam mounted on one limb and a single track pulley mounted on the other limb of the bow. One dual cam system includes two cams, each mounted on opposing limbs of a bow. Two cables and a single bowstring are strung between both cams, however, one end of each cable is yoked to an axle upon which a cam rotates. Another variant of the dual cam system, often referred to as a “cam and a half”, has one cable connected to a yoke at one end of that cable, and another cable connected to both cams.
One characteristic common to most cam systems, and compound bows in general, is that one or both cams include a single bowstring track within which the bowstring is guided, that is, let out and/or taken up, and at least one additional power cable track within which the upward moving power cable or the downward moving power cable is guided, that is, let out or taken up.
In many conventional cam systems, the bowstring moves in a single plane, and is generally guided in that single plane by the single bowstring track described above. The power cable(s) is/are offset laterally from the single plane in which the bowstring moves, and generally are guided in cable tracks that are offset to the left or right of the single bowstring track from the perspective of an archer holding or drawing the bow. When the bowstring is drawn during a draw cycle, loads are dynamically shifted from the bowstring to the cables. Due to the lateral offset of the power cable track and power cable from the single bowstring and single bowstring track, the cable loads are unbalanced relative to the longitudinal axis or central plane of the limbs. These unbalanced loads typically cause the cam to become overloaded on one side of a balance point, or generally unbalanced about the balance point, which results in a teeter totter effect on the limb, thereby causing it to twist or torque about its longitudinal axis. This problem is exacerbated when a cable guard is employed on the bow because the cable guard further offsets the cables from the limb's longitudinal central plane.
For example, with reference to FIGS. 1 and 1A, a conventional cam, including a bowstring track and a power cable track, is rotatably joined via an axle A to a limb L. The bowstring exerts a bowstring force BF, while the power cables exert power cable forces PCF. During the draw cycle, the bowstring force BF and power cable forces PCF are dynamically transferred, which changes the force distribution about a longitudinal axis/center line of the limb or balance point CL/BP. As a result, the force transfer and subsequent overload on one side of the center line or balance point CL/BP causes the cam to lean to that side, out of vertical alignment with the vertical plane P. The unbalanced cable load usually also causes the limb L to torque or twist an angle ∀ away from the horizontal plane HP as shown. The amount of lateral displacement of the unbalanced cable track to one side of the bowstring track, the vertical plane, or the CL/BP, also can contribute to the level or severity of the cam lean and resulting limb twist or torque.
The cam lean and limb twist generated by conventional compound bow cam assemblies can generate significant stress on the axle components and the bow limbs. Such frequent and significant longitudinal twisting also can accelerate fatigue and breakage of limbs. To compensate for such potential fatigue, some manufacturers make the limbs heavier, however, this typically results in a slower limb, and a slower shooting bow. In addition, the torque can impart an awkward feeling to the archer gripping the bow. This may distract the archer and cause the archer to over compensate when aiming.
The cam lean and limb twist common to conventional cam assemblies also present other issues for an archer shooting the bow. For example, cam lean can cause non-parallel nock travel in the windage or horizontal plane. This can cause inconsistent left and right point of impacts of arrows shot from the bow. Cam lean can also require an archer to position sight pins, of a sight mounted to the bow, off center from the arrow to be shot from the bow. For example, with conventional cam lean issues, archers frequently will mount the sight pins to the left of the center of the arrow on right-handed bows, and to the right of the center of the arrow on left-handed bows. In turn, this can exacerbate windage error and point of impact for longer range shots, and can complicate sight set-up.
While conventional compound bow cams can provide reasonably satisfactory performance, there remains room for improvement to reduce cam lean, bow limb twist and/or excessive cable wear due to the same.